Gamma knife radiosurgery for vestibular schwannoma: early hearing outcomes and evaluation of the cochlear dose.
OBJECTIVE
To evaluate the hearing outcomes for a group of unilateral vestibular schwannoma patients treated with gamma knife radiosurgery and to determine if the cochlear radiation dose affects hearing outcome measures.


METHODS
Retrospective case review.


METHODS
Tertiary referral center.


METHODS
Vestibular schwannoma patients (n = 33) treated with gamma knife with complete audiometric follow-up.


METHODS
Gamma knife radiosurgery and audiometry.


METHODS
Pure-tone average (PTA), speech discrimination score (SDS), and cochlear radiation dose.


RESULTS
The median audiometric follow-up was 24 months, with a range of 6 to 51 months (mean, 24.6 mo; standard deviation [SD], 13.9). Thirty-one patients received a maximum radiation dose of 26 Gy, and 2 received 24 Gy (mean, 25.9 Gy; SD, 0.48). All patients were treated to the 50% isodose line, and the prescription isodose was 13 Gy in 31 patients and 12 Gy in 2 patients (mean, 12.9 Gy; SD, 0.24). Mean pretreatment PTA and SDS were 55.86 dB and 45.70%, respectively. Mean PTA and SDS at last follow-up were 66.55 dB and 39.15%, respectively. The PTA at 6 months (p = 0.003), 12 months (p = 0.004), and last follow-up (p = 0.001) was significantly poorer than the pretreatment PTA. There was no significant difference between pretreatment and follow-up SDS at any time interval. The mean cochlear radiation dose was 5.2 Gy (range, 2.6-8.5 Gy). The median cochlear dose was 4.75 Gy. Fifteen patients received less than the median cochlear dose, and 18 received greater than or equal to the median cochlear dose. The change in PTA from baseline was significantly poorer at 12 months for those patients whose cochlea received 4.75 Gy (p = 0.02) or greater. Stepwise linear regression analysis using the variables of minimum SDS subsequent to baseline SDS versus total cochlear dose revealed a negative correlation (p = 0.012)-as total cochlear dose increased, SDS decreased.


CONCLUSIONS
The PTA was significantly worse after gamma knife radiosurgery, with a mean follow-up of 24.6 months. Higher radiation doses to the cochlear volume negatively impacted hearing outcomes after radiosurgery for this group of vestibular schwannoma patients.
Lasak
John M
JM
Department of Surgery, The University of Kansas School of Medicine, Wichita, Kansas, USA. Info@wichitaearclinic.com
Klish
Darren
D
Kryzer
Thomas C
TC
Hearn
Chris
C
Gorecki
John P
JP
Rine
Grant P
GP
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001299:Audiometry; D003051:Cochlea / Q000473:pathology* / Q000528:radiation effects / Q000601:surgery; D005260:Female; D005500:Follow-Up Studies; D006309:Hearing / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000601:surgery*; D011829:Radiation Dosage; D016634:Radiosurgery / Q000379:methods*; D012044:Regression Analysis; D012189:Retrospective Studies; D013063:Speech Discrimination Tests; D013067:Speech Perception; D013997:Time Factors; D016896:Treatment Outcome